1. Field of the Invention
The present invention relates generally to non-metallic honeycomb structures for use in situations where high thermal conductivity through the structure is required. More particularly, the present invention relates to improving the thermal conductivity of non-metallic honeycombs made from composite materials by including highly conductive pitch based carbon fibers within the honeycomb structure.
2. Description of Related Art
Honeycomb structures are well known and widely used in many applications where a high strength and light weight material is required. The combined features of light weight and strength found in honeycomb structures makes them particularly well-suited for use in aircraft. Honeycomb structures have been made from a wide variety of materials including metals, such as aluminum. Composite materials made from resin impregnated fibers and papers have also been widely used in honeycomb structures. These materials have been particularly well-suited for use in aircraft due to their light weight, high strength and stiffness. In addition to light weight and high strength, non-metallic honeycomb structures are good insulators which find use in aircraft structures where their insulating properties are beneficial.
Although the insulating properties of non-metallic honeycombs are desirable in many instances, there are situations where it is desired to have high strength, light weight materials which have a high thermal conductivity. For example, jet aircraft engines require a high degree of thermal transfer through the engine structure in order to maintain structural temperature loads at acceptable levels. Accordingly, the engine structure from the hot core to the outer nacelle must have high thermal conductivity while still being extremely strong and light weight.
Honeycomb structures made from aluminum are strong and have sufficient heat conductivity to transfer the necessary heat load from the hot core to the outer nacelle. However, aluminum core, in conjunction with graphite fiber reinforced composite skins, is subject to corrosion problems. Various glass fiber reinforced composite honeycomb structures and polyacrylonitrile (PAN) based carbon fiber reinforced composite materials have been suggested as potential substitutes for the aluminum honeycomb structures in jet aircraft engines. However, such non-metallic honeycomb structures are not suitable due to their poor thermal conductivity.
In view of the above, it would be desirable to provide non-metallic honeycomb structures which have increased thermal conductivity so that such structures could be used in applications where high heat transfer rates are required. It would further be desirable to provide such a high thermal conductivity non-metallic honeycomb structure wherein the desirable features of structural strength and light weight are maintained while minimizing cost.